There is some combination of install that causes the ASP.NET 2.0 web service extension to be missing from the Web Services Extension page in IIS 6. I think it is caused by installing IIS services after the 2.0 framework is installed.
In order to get it to appear, run
[code language="vb.net"]
aspnet_regiis.exe -i
[code]
from the command line. This will re-install 2.0, and fix the issue. 'aspnet_regiis.exe' is located in the C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727 folder. I usually navigate there in Windows Explorer, create a .bat file with the above command in it and run it that way.
As always, your comments are welcome.